The invention relates to a method for the production of a stamping with an enlarged functional surface, especially fine blanking a workpiece out of a flat strip, wherein the flat strip at closing is clamped between an upper part consisting of a shearing punch, a pressure pad for the shearing punch, an arranged on the pressure pad V-shaped projection and an ejector and a lower part consisting of a cutting die and an ejector and the V-shaped projection is pressed into the flat strip.
The invention further relates to devices for the production of a stamping with an enlarged functional surface, especially fine blanking a workpiece out of a flat strip, with a tool having two parts comprising at least a shearing punch, a pressure pad for the shearing punch, an arranged on the pressure pad V-shaped projection, an ejector, a cutting die and an ejector, wherein the flat strip is clamped between pressure pad and cutting die and the V-shaped projection is pressed into the flat strip.
Fine blanking and forming techniques are mainly used to process different steels. Within this, the multiplicity of used materials comprises general-purpose construction steels up to high-tensile fine-grained steels. The resource “material” during the last years gained large importance. With an optimal material utilization, the production costs of a component can be significantly influenced. The high-tensile steels allow for components with thinner walls with the same strength behavior.
In most of the cases, the cutting surface at fine blanking acts as a functional surface, and that is why the rollover is a cost factor.
Typical features of fine blanking parts are the edge rollover and the cutting burr. Especially in corner areas, the rollover occurs, and grows with decreasing corner radius and increasing sheet thickness. The depth of the rollover can be about 30%, and the width of the rollover, about 40% of the sheet thickness or more (see DIN 3345, Feinschneiden, August 1980). Thus the rollover depends on material thickness and quality, so that the possibility to control it is limited and often brings about a limited function of parts, for example, due to a lack of sharp edges of the corners at toothed parts or the caused change in the functional length of the parts.
The stamping rollover thus reduces the functionality of parts and urges the manufacturer to use a thicker raw material.
A number of solutions for trying to get rid of the edge rollover either by re-cutting (CH 665 367 A5), shaving (DE 197 38 636 A1) or shifting of material during the cutting (EP 1 815 922 A1) are known.
The known solutions according to CH 665 367 A5 and DE 197 38 636 A1 do not reduce the edge rollover, but largely rework the parts, so that on the one hand, significant costs for additional machining operations and tools are required and, on the other hand, a respective loss of material occurs due to the necessity of using thicker materials.
In the known solution according to EP 1 815 922 A1, the workpiece is machined in a single-step setup in at least two chronologically successive steps in different cutting directions, wherein during a first cutting process in a vertical working direction, a semi-finished product corresponding to the geometry of the workpiece with small rollover is cut out, and finally cut during at least one further cutting process in the opposite working direction. The rollover of the first partial step with this shall be filled up again at least in the corner area. But with this known method in the first instance, the projecting stamping burr is avoided. Also with this known solution, the rollover lastly is not avoided and material volume is shifted along the cutting line, which is accompanied by an increased risk of tearing.
At this state of the art, it is an object of the invention to largely, systematically avoid the edge rollover by creating a rollover corresponding to the volume within the part geometry, and at the same time, to maintain the functional surfaces at thinner fine blanking parts and to save material, without material being shifted along the cutting line.